The present invention relates to a drive shaft for rolls in rolling mills and the like, more particularly to a drive shaft for connecting a drive shaft element to the roll neck portion of a rolling mill to drive the roll, the drive shaft incorporating two universal joints to maintain the drive shaft element in alignment with the roll serving as a driven shaft element.
Generally, drive shafts of this type are provided at the opposite ends with fitting yokes to be axially fitted to the end of a drive shaft element and to the end of a driven shaft element to connect the drive shaft to these shaft elements so that the drive shaft can be easily disconnected from the shaft elements for the replacement of the roll or the like.
FIG. 1 shows a conventional drive shaft. A shaft member B connected to a drive fitting yoke A by a joint member J.sub.1 is splined to a shaft member D connected to a driven fitting yoke C similarly by a joint member J.sub.2 for the transmission of torque as well as for axial sliding movement. Further as shown in FIG. 1, the drive fitting yoke A is connected to a drive shaft element G as by shrinkage fit with a key K also fastening the yoke to the drive shaft element G for the transmission of torque and also for preventing the axial movement of the yoke. The drive fitting yoke C is secured to a driven shaft element H by a bolt F or an unillustrated pin. During the rotation of the drive shaft, the shaft members B and D are slidable relative to each other with the shaft members B and D fitted and connected to the drive shaft element G and to the driven shaft element H respectively.
However, the drive shaft during rotation undergoes vibration or oscillation due to variations in the load or for some other cause, resulting in loosening, break or wear of the bolt F or pin and leading to improper shaft connection. Because the shaft members B and D are adapted for free sliding movement, the driven fitting yoke C will then slip off from the driven shaft element H, with the result that the rolling operation stops inavertently, thereby reducing the operating efficiency.
To overcome the foregoing drawback, another drive shaft as shown in FIG. 2 has been proposed. It is seen in FIG. 2 that the shaft members B and D are respectively provided with annular projections B.sub.1 and D.sub.1 each on the outer periphery of the shaft member, and a spring M is provided between the annular projections B.sub.1 and D.sub.1 to bias the shaft members B and D away from each other, such that the force of the spring M acts to fit the drive fitting yoke A to the drive shaft element G and the driven fitting yoke C to the driven shaft element H when connecting the drive shaft to the shaft elements. With the drive shaft thus mounted in place, the spring M acts similarly also during the rotation of the drive shaft so as to hold the driven fitting yoke C connected to the driven shaft element H against the rotational oscillation of the shaft. This structure eliminates the need for the bolt F shown in FIG. 1 or pin used for securing the driven fitting yoke C to the driven shaft element H, thus rendering the drive shaft easier to mount and dismount.
With the drive shaft shown in FIG. 2, however, the spring M has a large diameter because it is provided on the outer periphery of the drive shaft. Accordingly, the wire of the spring M must have an increased diameter in order to ensure a suitable spring force and a suitable amount of compression or expansion, but the swing diameter of the drive shaft is limited in the case of rolling mills. Thus, the limitations imposed on the diameter of the drive shaft and on the wire diameter of the spring M render the spring M difficult to design. Moreover, an increase in the diameter of the wire of the spring M entails the necessity of reducing the inside and outside diameters of the shaft member B to enable the shaft member B to retain its strength, further making it necessary to reduce the diameter of the spline coupling portion E between the shaft members B and D. This leads to an increase in the surface pressure acting in the direction of rotation on spline coupling portion E per spline tooth, thereby giving rise to increased resistance against the sliding movement involved and greatly deteriorating the strength of the spline coupling portion E. As a result, the drive shaft has reduced strength and a lowered torque transmitting capacity. The proposed drive shaft has another serious drawback that the force of the spring M acting to move the shaft members B and D away from each other is delivered by way of the joint members J.sub.1, J.sub.2 and fitting yokes A, C to the drive shaft element G and to the driven shaft element H to which the drive shaft is connected, consequently subjecting the shaft elements G, H to a thrust load at all times. The spring force thus acting on the joint members J.sub.1, J.sub.2 and further on the drive and driven shaft elements G, H subjects the joint members J.sub.1, J.sub.2 and the bearings supporting the shaft elements G, H to an excess thrust load, thereby greatly impairing the performance of the joint members and of the bearings. Thus, the drive shaft shown in FIG. 2 involves difficulties in the design and in the strength and has the drawbacks that it is not durable to use and adversely affects the neighboring mechanical parts associated therewith.